1. Field of the Invention
The present invention relates generally to an automotive power train including an automatic transmission which is coupled to a supercharged internal combustion engine, and more specifically to a transmission shift shock attenuation arrangement which controls both the engine ignition and the supercharge pressure produced by a turbocharger.
2. Description of the Prior Art
It is known to combine engine ignition timing control with transmission shifting for the purposes of reducing shift shock. However, in the case of engines which are equipped with superchargers or turbochargers, and the shift shock attenuating control arrangement is applied only to the engine ignition, a problem has been encountered in that the cylinder pressure tends to be higher than in the case of naturally aspirated engines.
In the case wherein the ignition is retarded to a level relatively close to TDC in supercharged engines, the cylinder pressure tends to increase to relatively high levels.
As a result of this higher pressure, a higher voltage which must be applied to the electrodes of the spark plug or plugs which are exposed to the combustion chamber in order to induce the spark to actually are across the spark plug electrodes. This of course tends to invite misfiring with attendant increases in vibration and noxious emissions.
However, in order to provide the required high voltage a further problem is experienced in that it becomes necessary to prevent leakage from the high tension cords which form part of the ignition system. This requires that the spark plug peripheral clearance be set at a relatively large value.
Accordingly, it has been very difficult in actual practice to obtain the desired engine output control simply by retarding the ignition in supercharged engines.
Further, when it has been attempted to achieve a reduction in the output of the engine by simply reducing the supercharge pressure, the response characteristics of the engine have tended to deteriorate to the degree that shock attenuation is again rendered inadequate.